1. Field of the Invention
The present invention relates to the production of the novel dispersants and the sizing agent dispersions produced therefrom which are advantageously employed for sizing paper. The invention further relates to cationic dispersants for the dispersion of sizing agents, for example rosins and/or derivatives thereof, and reactive sizing agents, for example alkyl ketene dimers, as well as cationic sizing agent dispersions containing these dispersants and possibly also aluminum sulfate.
2. Technology Review
Aqueous resin dispersions for sizing paper are known. Resin dispersions based on natural resins, e.g. rosin resins, possibly containing polymers such as starches that have been crosslinked, possibly under alkali conditions, with methyl cellulose, casein or other proteins are disclosed in many patents. For example, resin dispersions made according to the Bewoid process, are mentioned in German Patent No. 1,131,348. U.S. Pat. No. 3,955,654 describes resin dispersions produced by high pressure homogenization.
Also known are cationic dispersions of paper sizing agents in water in which cationic starches or cationic, synthetically produced polymers are usually employed as the cationically active substances. The presence of the cationically active substances considerably accelerates the sizing process.
U.S. Pat. No. 3,966,654 discloses aqueous dispersions of paper sizing agents in water which are composed of 5 to 50 weight percent of a fortified resin, 0.5 to 10 weight percent of a water-soluble cationic dispersant and water. The fortified resins employed here are primarily wood and tall oil rosins which have been reacted with compositions containing the group &gt;C.dbd.C--C.dbd.O. The cationic dispersant may be polyamine epichlorohydrin resins, alkylene polyamine epichlorohydrin resins or polydiallylamine epichlorohydrin resins. The disadvantages of these dispersions are that their shelf life stability still leaves something to be desired.
Aqueous dispersions of finely dispersed and fortified resin sizing agents are the subject matter of U.S. Pat. No. 4,374,673 which is related to European Patent 0,056,876. Instead of the dispersants disclosed in U.S. Pat. No. 3,966,654, this process employs cationic starches as the water-soluble dispersants. Moreover, they also contain an anionic surfactant. The remainder of the dispersion is water. The dispersions employed for sizing paper can be produced either by homogenization of a solution or melt of the fortified resin in a homogenizer under pressure or according to the so-called inversion process. In the first-mentioned process, the fortified resin is initially dissolved in an organic solvent that is not water-miscible. Thereafter, the aqueous solution of a cationic dispersant and an anionic surfactant are dispersed in the solution. By homogenization in a homogenizer under pressures of 50 to 400 bar, the unstable emulsion becomes a stable emulsion. Finally, the organic solvent is removed by vacuum distillation.
Paper sizing agents based on rosin dispersions are also disclosed in European Patent Publication 200,002. In addition to rosin, which may be modified with maleic acid anhydride, fumaric acid, or a modified hydrocarbon resin, these sizing agents contain commercially available protective colloids or surfactants, polyaluminum hydroxychlorides and possibly retention, fixing agents, and/or wet-strength imparting agents. Because of their poor electrolyte stability, these dispersions tend to undergo phase separation and to thicken.
Laid-open application DE 3,737,615 discloses a resin emulsion sizing agent which is composed of a fortified resin and an at least partially quaternary copolymer composed primarily of a monomer of a (meth)acrylic acid alkyl amino alkyl ester or amide and water. An alleged advantage of this sizing agent is that, at a higher pH, in harder water and at a higher temperature (that is, under conditions in which the conventional anionic sizing agents no longer perform efficiently) it has a good sizing effect. This sizing agent is, however, incompatible with acid aluminum salts.
It is therefore an object of the present invention to provide stable sizing agent dispersions for sizing in the neutral and weakly alkali range which are suitable for internal sizing or only the surface, are additionally well compatible with aluminum sulfate and can be manufactured economically without the need for an expensive stirring assembly or other apparatus.